Universal Mobile Telecommunications System (UMTS) is a 3G mobile communication system using Wideband Code Division Multiple Access (WCDMA) air interface technology, and is mainly developed in WCDMA/GSM (Global System for Mobile Communications) global standardization organization for Third Generation Partnership Project (3GPP).
In the 3GPP UMTS standards, depending on whether a Radio Resource Control (RRC) connection has been established, a User Equipment (UE) may be classified into Idle mode and RRC Connected mode. The UE which has not established the RRC connection with UMTS Universal Terrestrial Radio Access Network (UTRAN) is in Idle mode, and the UE in this mode may only be identified with Non-Access Stratum (NAS) identification, for example, be identified with International Mobile Subscriber Identity (IMSI); and when the UE which has established the RRC connection with UTRAN is in RRC Connected Mode, a Radio Network Temporary Identity (RNTI) allocated for the UE in this mode is taken as an identification on a public transport channel for the UE.
And the UE in RRC Connected Mode may be further separated into different states depending on the levels of the RRC connection and the transport channel types available for the UE: the UE in CELL_PCH state, CELL_FACH state and CELL_DCH state may be identified at cell level, and the UE in URA_PCH state may be identified at UTRAN Register Area (URA) level. A dedicated physical channel is allocated for the UE in CELL_DCH state, and the UE may use the dedicated transport channel, a shared channel and their combination. The UE in CELL_FACH state continuously monitors a Forward Access Channel (FACH) in downlink and a default Reverse Access Channel (RACH) is allocated for the UE in uplink. The UE in CELL_PCH state and URA_PCH state uses Discontinuous Reception (DRX) approach for monitoring a Page Channel (PCH) via an associated Page Indicator Channel (PICH), and the UE in these two states has no uplink activity.
In the 3GPP UMTS standards, when a UE is in different modes and states, it will measure an inter-frequency cell in response to the received measurement control information or system information and the receiving quality of the cell in which the UE is located to perform cell reselection and cell switching etc. For the UE in Idle, CELL_PCH, URA_PCH and CELL_FACH states, the conditions for triggering inter-frequency cell measurement are received system information and the receiving quality of the current cell in which the UE is located; while for the UE in CELL_DCH state, the condition for triggering inter-frequency cell measurement is the measurement control information sent by the system. In general, a UE without dual receivers cannot simultaneously receive and decode signals of two different frequencies, so the UE will interrupt the signal reception in the current cell during performing inter-frequency cell measurement.
The 3G mobile communication system introduces a concept of broadcast and multicast for efficient utilization of mobile communication network resources, and the multicast and broadcast service is a technology for transmitting the same data from one data source to multiple destinations. Therefore, WCDMA/GSM global organization for standardization 3GPP puts forward Multimedia Broadcast/Multicast Service (MBMS). The MBMS refers to providing a point-to-multipoint service for transmitting the same data from one data source to multiple users in a mobile communication network, so as to realize network resource sharing and improve network resource utilization, especially the utilization of air interface resources.
The data transmission of the MBMS service between the UE and the UTRAN may be divided into two modes: Point to Point (PTP) and Point to Multipoint (PTM). The PTP mode is used for MBMS multicast mode. The UE of RRC Connected Mode in multicast mode receives control information via a Dedicated Control Channel (DCCH) and receives service information via a Dedicated Service Channel (DTCH). While the PTM mode is used for MBMS broadcast or multicast mode, the UE in this mode receives data information via an MBMS point-to-multipoint Traffic Channel (MTCH) and receives control information via an MBMS point-to-multipoint Control Channel (MCCH).
The cells monitored by the UE may be classified into the following three categories:    1) Active Set cell: the UE information is transmitted in these cells; the UE only measures the Active Set cells contained in a list of cell information;    2) Monitor Set cell: the cells not contained in the Active Set cells but contained in the list of cell information are monitor Set cells;    3) Detection Set cell: the cells neither contained in the list of cell information nor contained in the Active Set cells, but may be detected by the UE are Detection Set cells.
When a dual mode UE supporting WCDMA Frequency Division Duplex (FDD) mode and WCDMA Time Division Duplex (TDD) mode in CELL_FACH state performs inter-frequency measurement to a TDD cell in FDD mode, in order to identify a new TDD cell or measure Received Signal Code Power (RSCP) of a Primary Common Control Physical Channel (PCCPCH) for TDD cell reselection between systems, it will position a frame whose System Frame Number (SFN) satisfies the following formula and perform TDD cell inter-frequency measurement in the frame.SFN div N=C_RNTI mod M_REP+n×M_REP  (formula 1)
In which:
N represents the number of 10 ms frames of Transmission Timing Interval (TTI) of the FACH with a maximal TTI on an Secondary Common Control Physical Channel (SCCPCH) bearing non-MBMS logical channel monitored by the dual mode UE;
M_REP represents the measurement interval cycle period, M_REP=2k; and according to the above formula, the repeat period of the measurement time for N frames is N×M_REP frames; k is the coefficient of FACH Measurement interval cycle period, which may be read from the information element “FACH measurement occasion info” contained in the system information 11 or 12;Cell Radio Network Temporary Identity (C_RNTI) represents the C_RNTI value of the dual mode UE;n=0, 1, 2 . . . , as long as the SFN is less than its maximum value.
When the dual mode UE supporting WCDMA FDD mode and WCDMA TDD mode in CELL_DCH state performs inter-frequency measurement to a TDD cell in FDD mode, in order to identify a new TDD cell and measure the PCCPCH RSCP for switching TDD cell between systems, it will perform inter-frequency measurement to the TDD cell in a compression mode indicated by the UTRAN, and the technical principle of the compression mode is shown in FIG. 1, i.e. when the UTRAN transmits certain frames (the data transmitted every 10 ms is one frame), the data transmission rate is increased, and the data previously transmitted in 10 ms may be transmitted less than 10 ms, then the saving time will be used to perform inter-frequency measurement for the dual mode UE, but when and how to increase the transmission rate is completely controlled by the UTRAN.
In the prior art, the main process for the dual mode UE supporting WCDMA FDD mode and WCDMA TDD mode in CELL_FACH state performing inter-frequency measurement to the TDD cell in FDD mode is as follows:    1) the UE triggers the inter-frequency measurement for the TDD cell according to the system information and the cell receiving quality;    2) the UE performs inter-frequency measurement to the TDD cell within the measurement time calculated through the Formula 1 (for example, when the UE receives the MBMS PTM service, it will interrupt the measurement to ensure demodulation performance of the received MBMS, so the measurement time will not reach the measurement time calculated through the Formula 1);    3) the physical layer of the UE reports the inter-frequency measurement result to the upper layers of the UE; or identifies a new TDD cell using the inter-frequency measurement result.
In the prior art, the main process for the dual mode UE supporting WCDMA FDD mode and WCDMA TDD mode in CELL_DCH state performing inter-frequency measurement to the TDD cell in FDD mode is as follows:    11) the UE triggers inter-frequency measurement to the TDD cell according to the measurement control information sent from the UTRAN system;    12) the UE performs inter-frequency measurement to the TDD cell within the measurement time indicated by the compression mode sent from the UTRAN;    13) the physical layer of the UE reports the inter-frequency measurement result to the upper layers of the UE; or identifies a new TDD cell using the inter-frequency measurement result.
In summary, when the dual mode UE supporting WCDMA FDD mode and WCDMA TDD mode performs inter-frequency measurement to the TDD cell, the measurement time is calculated through the above-mentioned Formula 1 or indicated by the compression mode sent from the UTRAN, thus the measurement performance is evaluated by taking the measurement time calculated through the Formula 1 or the measurement time indicated by the compression mode sent from the UTRAN as valid measurement time.
But in practice, TDD system is Time Division Duplex mode, the receiving data and the transmitting data need to be respectively born in different timeslots of a same channel (i.e. carrier), and guard intervals (i.e. Guard Period, a time interval existing between timeslots and having a length much shorter than that of a timeslot) are used for separating different timeslots. In the TDD system, the broadcast channel bearing the system information only exists in a dedicated downlink timeslot. And 3G UMTS standard supports two categories of TDD systems.
The first is 3.84 Mcps TDD system, the system frame structure of which is shown in FIG. 2. Each 10 ms frame includes 15 timeslots, and each of the 15 timeslots is transmitted by uplink or downlink. However, among these 15 timeslots, at least one timeslot is allocated as downlink and at least one timeslot is allocated as uplink.
The second is 1.28 Mcps TDD system, each 10 ms frame in the system is divided into two 5 ms subframes, a structure of the subframe is shown in FIG. 3, and each subframe includes 7 timeslots.
In a 3.84 Mcps TDD system, the PCCHPCH mapped from the broadcast channel bearing the system information only exists in one downlink timeslot of one frame; while in a 1.28 Mcps TDD system, the PCCHPCH mapped from the broadcast channel bearing the system information only exists in Timeslot 0 of each subframe.
It is obvious that in a TDD system, the PCCPCH mapped from the broadcast channel bearing system information only exists in a dedicated downlink timeslot, while the inter-frequency measurement for the TDD cell performed by the dual mode UE for identifying a new TDD cell or getting the PCCPCH RSCP measurement result only aims at the timeslot in which the PCCHPCH mapped from the broadcast channel bearing the system information is located. So, when the dual mode UE operating in the FDD mode cannot receive or cannot completely receive the timeslot in which the PCCHPCH mapped from the broadcast channel bearing the system information is located within the measurement time calculated through the Formula 1 or indicated by the compression mode sent from the UTRAN, it is insignificant to directly take the measurement time calculated through the Formula 1 or the measurement time indicated by the compression mode sent from the UTRAN as valid measurement time. Therefore in the prior art, when the dual mode UE operating in the FDD mode performs inter-frequency measurement to the TDD cell, the evaluated measurement performance is not accurate sometimes because the measurement time calculated through the above-mentioned Formula 1 or the measurement time indicated by the compression mode sent from the UTRAN is directly taken as valid measurement time for evaluating the measurement performance while not considering the frame structure of the TDD) system.